Applying Bilateral Filter

void bilateralFilter(InputArray src, OutputArray dst, int d, double sigmaColor, double sigmaSpace, int borderType=BORDER_DEFAULT )

Parameters:
  • src – Source 8-bit or floating-point, 1-channel or 3-channel image.
  • dst – Destination image of the same size and type as src .
  • d – Diameter of each pixel neighborhood that is used during filtering. If it is non-positive, it is computed from sigmaSpace .
  • sigmaColor – Filter sigma in the color space. A larger value of the parameter means that farther colors within the pixel neighborhood (see sigmaSpace ) will be mixed together, resulting in larger areas of semi-equal color.
  • sigmaSpace – Filter sigma in the coordinate space. A larger value of the parameter means that farther pixels will influence each other as long as their colors are close enough (see sigmaColor ). When d>0 , it specifies the neighborhood size regardless of sigmaSpace . Otherwise, d is proportional to sigmaSpace .
You can find a nice example in OpenCV Documentation.

A bilateral filter is non-linear, edge-preserving and noise-reducing smoothing filter. The intensity value at each pixel in an image is replaced by a weighted average of intensity values from nearby pixels. This weight can be based on a Gaussian distribution. Crucially, the weights depend not only on Euclidean distance of pixels, but also on the radiometric differences. For example, the range difference such as color intensity, depth distance, etc. This preserves sharp edges by systematically looping through each pixel and adjusting weights to the adjacent pixels accordingly.

Example:

 ------------
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"

using namespace std;
using namespace cv;

int main( int argc, char** argv )
 {
  
     Mat src = imread( "Fig1039.tif", 1 );
     Mat dst;

     //Apply bilateral filter
     bilateralFilter ( src, dst, 15, 80, 80 );
     imshow("source", src);
     imshow("result", dst);  

     waitKey(0);
     return 0;
 }

------------

Result:


Source:
http://en.wikipedia.org/wiki/Bilateral_filter

2 comments:

  1. How do you actually determine d,sigmaColour and sigmaSpace for any application ? Should it be done by looking at the image histogram ? Or should be done on a trial and error basis ?

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    Replies
    1. http://docs.opencv.org/3.0-beta/modules/imgproc/doc/filtering.html

      this is by opencv for learning about filters and it explains what the values are.

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